On Windows objcopy fails to split debug info with --only-keep-debug when this debug information is bigger than 2 GB.

This is because of the following code in bfd_malloc():

  if (size != sz
      /* This is to pacify memory checkers like valgrind.  */
      || ((signed long) sz) < 0)
    {
      bfd_set_error (bfd_error_no_memory);
      return NULL;
    }

On mingw32 target sizeof(long) is 4 bytes which makes < 0 condition invalid.